With constant increase of the capacity of DC power systems, DC transmission and transformation technologies are developed vigorously. This demands a higher system stability and security. Among various faults possibly occurring to a power system, short-circuit fault is most hazardous to the power grid and has a high probability to occur. Short-circuit of DC systems will cause a current peak to rise to a very high level is a short time. Therefore, short-circuit cutoff and protection is an important issue in the development of DC systems. Difficulties in DC breaking are mainly manifested in two aspects. One aspect is that a DC does not have a natural zero crossing point like an AC, such that it is very difficult for current to pass through zero point and a current zero crossing points needs to be artificially created. The second aspect is that a DC breaker has to absorb tremendous energy during separation of the short-circuit current. A currently common solution is to effectuate current breaking by establishing a reverse voltage through a transfer capacitor or an electronic device that can be turned off. The transfer capacitor scheme mainly has a large size but a long small-current separating time and needs a complex charging-discharging device, while the full-controlled power electronic device scheme mainly has a complex control and a high cost and needs a complicated water-cooling system. Therefore, the followings have become core issues that restrict development of circuit breakers: how to simplify the structure of a DC circuit breaker, reduce cost and size, improve transfer efficiency, and effect fast breaking of different levels of current.